If a chart report handed you this aspect, the report is wrong. Here is what you are probably looking at.
What it looks like in a life
The closest real version is a wide conjunction: Mercury twenty to twenty-eight degrees from your Sun, often in the sign next door. That feels like cooperation rather than fusion, because your mind and your identity are related without being identical. A Sagittarius Sun with a Capricorn Mercury thinks in a different key than it lives in.
The gift
The wide version is the useful one. You can hear your own thoughts as thoughts instead of as self, which is the closest thing this pair gives you to perspective.
The friction
It also splits you slightly. The way you explain your life and the way you live it do not quite match.
The esoteric layer
Hellenistic practice read this pair by sign and by distance from the Sun. No tradition assigned meaning to an angle that Mercury's orbit cannot produce.
Where this goes
Check Mercury's actual degree and sign. A full natal reading reads the pair as it really sits and tells you which side is running you.
Related
See it in your own chart
Cast your chart free and read this placement next to everything else you carry.